As long as the solar collector is able to keep the tank temp above ITS set point, the element will never come on. The only reason to have an element in the tank at all, is to guarantee enough heat to make a < 100 amp tankless sufficient, even in the dead of winter, when the solar isn't saving me anything anyhow.

I'm planning to use my existing 50 gal tank with an external heat exchanger and see how that does. If it's not enough, I can always upgrade later.

Yes were are missing each other.

The point is, why have solar hot water if the tanked water heater is already heating the water? The pump on the solar hot water system will never come on if there is already hot water in the tank.

Setting this up like you intend is a waste of time and resources.

It would be as efficient as sending it to me.

Want my address?

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My idea of a perfect day: No where to go and all day to get there.

People run solar tanks upwards of 180* all the time. That's what tempering valves are for.

I suspect you could be getting a lot more out of your solar setup than you are...

My solar hot water system runs at 180. But I also have a much more robust system than you will. My heat exchanger is open and not pressurized and has over 500 gallons of water in one tank and 275 in another. I just got a 1000 gallon tank for $100 and intend to put that in service.

I can heat my water and my home with what I have right now unless the sun doesn't shine for a few days.

Once the hot water in my hot water tank (120 gallons) reaches 140 degrees the valve closes and the water is returned to the solar panel unless I need heat in the house, then it is routed through the heat pipes and my modified A coil till the house is warm enough.

When there is no sun I can heat my home and hot water for over 3 days.

If the delta T between the solar panels and the storage tank drops below 15 degrees the pump shuts off.

With 110 sg ft of solar panels I have more hot water than I know what to do with.

I think I get a lot more out of my system that just about any one else's system in the world. Most solar hot water systems don't have enough storage and they lose a lot of potential heat. Mine runs so well I don't have an electric water heater that is hooked up. I suppose that if the weather gets so bad that the sun doesn't shine for a week or so I might have to hook up the hot water tank but so far I haven't had a need for it in 5 years.

Once I get my 1000 gallon tank in the system I should be good to go for 2 weeks without sun.

Wanna hear the good part. I don't have more than $1500 into my system.

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My idea of a perfect day: No where to go and all day to get there.

My solar hot water system runs at 180. But I also have a much more robust system than you will.

How do you know how robust my system will or will not be? As far as I know there's no problem putting 180* water in a plane old water heater, as long as you install a proper expansion tank.

Quote:

Originally Posted by Marvin Gardens

Once the hot water in my hot water tank (120 gallons) reaches 140 degrees the valve closes and the water is returned to the solar panel unless I need heat in the house, then it is routed through the heat pipes and my modified A coil till the house is warm enough.

So I'm confused. You say your system runs at 180*, but then you say your tank doesn't get above 140*. Huh?

Quote:

Originally Posted by Marvin Gardens

With 110 sg ft of solar panels I have more hot water than I know what to do with.

Yeah, I bet. That is A LOT of collector area.

Quote:

Originally Posted by Marvin Gardens

I think I get a lot more out of my system that just about any one else's system in the world.

But it takes 110 Ft^2 and a lot of water storage to do it. Geez.

Quote:

Originally Posted by Marvin Gardens

Wanna hear the good part. I don't have more than $1500 into my system.

Are you using home made flat plates? I'm planning to spend the extra cash on evacuated tubes because they work better in cold weather and indirect sun light. If I was in a dryer/hotter climate, I'd use flat plates as well.

What happens when your tanks get below 140? Does your water just get cooler and cooler until the sun comes out? I don't mind paying a few bucks a month during the winter to ensure that I always get 140* at the tap. I can always upgrade the tank (or add one) if I feel it doesn't store enough heat. And, if I heat the tank to 180*, that's a lot of reserve I can burn through before the tankless ever has to kick on.

How do you know how robust my system will or will not be? As far as I know there's no problem putting 180* water in a plane old water heater, as long as you install a proper expansion tank.

I know because I have seen a lot of systems and none of them have even come close to my heat production.

Plus it is all controlled by a computer and radio controlled temperature sensors that control all the solenoid valves.

Quote:

Originally Posted by gp_wa

So I'm confused. You say your system runs at 180*, but then you say your tank doesn't get above 140*. Huh?

My storage tanks get to 180. My water tank for bathing and showers are set for 140.

Quote:

Originally Posted by gp_wa

Yeah, I bet. That is A LOT of collector area.

But it takes 110 Ft^2 and a lot of water storage to do it. Geez.

This is why my system will probably be more robust that yours. Most people don't a have 7 panels because of the lack of room.

Quote:

Originally Posted by gp_wa

Are you using home made flat plates? I'm planning to spend the extra cash on evacuated tubes because they work better in cold weather and indirect sun light. If I was in a dryer/hotter climate, I'd use flat plates as well.

I got them all on craigslist for free or next to free. I had to rebuild several of them since the insulation was toast.

Evacuated tubes are nice. They work on ultraviolet which is around even on cloudy days.

But too expensive for me. I am cheap and prefer to heat my water as cheap as I can.

Quote:

Originally Posted by gp_wa

What happens when your tanks get below 140? Does your water just get cooler and cooler until the sun comes out? I don't mind paying a few bucks a month during the winter to ensure that I always get 140* at the tap. I can always upgrade the tank (or add one) if I feel it doesn't store enough heat. And, if I heat the tank to 180*, that's a lot of reserve I can burn through before the tankless ever has to kick on.

It does get cold. I have never had that happen in 5 years but there is no contingency plan. I guess I could hook up the hot water tank if needed.

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My idea of a perfect day: No where to go and all day to get there.

A simple tempering valve would allow you to run the domestic hot water tank to 180 as well.

Not really necessary.

I have over 700 gallons of 180 degree water now and when I put in the 1000 gallon tank I will have 1700 gallons of 180 degree water which is equal to roughly 500 KW of power in heated water and another 120 gallons of water that is 40 degrees warmer is not going to make much difference.

That's only 10 KW more energy which is only a 2% increase.

If I needed more heat I would just get another big tank.

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My idea of a perfect day: No where to go and all day to get there.